You have to identify the register that vim is using to get the outside clipboard.
First copy any text outside vim and then inside vim do the command :registers and look for the text you copied, once you have identified the register simply use it every time you need to copy and paste from the outside:
for example:
Im using gvim in Windows7 and the register used by vim to get the external clipboard is
*"
then in vim select the text and do
*"y
to copy (yank) and paste outside as usual
and to paste inside vim from outside do *"p
you can also do a map to the register to easy copy/paste